Re: Strangeness in ASRT

[Stefan Monnier <monnier@iro.umontreal.ca>]

> This seems to have a bug which breaks compilation.
>     /* The IDX==IDX tries to detect when the macro argument is side-effecting.  */
>     #define ASET(ARRAY, IDX, VAL)	\
>       (eassert ((IDX) == (IDX)),				\
>        eassert ((IDX) >= 0 && (IDX) < ASIZE (ARRAY)),	\
>        ASLOT ((ARRAY), (IDX)) = (VAL))

> Changing ASLOT to AREF makes it compile.  (Bootstrapping still crashes
> as before.)

Oh, yes, it should be AREF, not ASLOT.  Sorry for the mixup.

> What is the purpose of these tests?  The expansion of AREF
> substitutes IDX only once, so there is no problem if it has
> a side effect.

If ENABLE_CHECKING is true, then eassert ((IDX) >= 0 && (IDX) < ASIZE
(ARRAY)) will cause IDX to be eval'd several times, so you'll get errors
when you set ENABLE_CHECKING and an argument has the form "index++".


        Stefan